Production and treatment of soap



United States Patent US. Cl. 260-418 12 Claims ABSTRACT OF THEDISCLOSURE This invention relates to a process for the production of asoap of improved colour and odour which includes the step of treating asoap containing system at any stage during the production of the soapwith an alkali metal borohydride at a pH of at least 9.5. The soapcontaining system is preferably treated With anaqueous alakli solutioncontaining 0.01-0.30% sodium borohydide by weight of the fat chargeimmediately after it leaves the washing unit.

This invention relates to a process for the preparation of a soap and,in particular, it relates to a process for the preparation of a soap ofimproved colour and odour.

It is known that certain of the coloured compounds present in low gradefats or fatty acids are not removed by a conventional treatment withactivated adsorbent materials. The characteristic odour of unperfumedsoap is also diflicult to remove by treatment of the fat or fatty acidwith an activated adsorbent material. Of the various solutions that areapplicable to the problem of removing these coloured compounds andodoriferous compounds which are not satisfactorily absorbed, that ofchemical reduction seems to have been given some consideration, buthitherto has not met with any great practical success.- Application ofnon-selective reducing treatments (for example hydrogenation in thepresence of a nickel catalyst) does not provide a useful solution as theremoval of colour and odour requires an undesirable increase in themelting point of the fat charge. Furthermore, specialized pressurevessels are required to carry out this hydrogenation treatment.

Certain reducing agents, such as the alkali metal borohydrides, areknown to decompose at elevated temperatures in aqueous solution, therate of decomposition increasing with increasing temperature anddecreasing with increasing alkalinity of the solution. In view of thisknowledge, it is surprising to find that low concentrations of alkalimetal borohydride can rapidly reduce the colour and odour of a viscousmedium like molten soap.

Accordingly this invention provides a process for the preparation of asoap which includes the step of treating a soap containing system at anystage during the manufacture of the soap with an alkali metalborohydride, at a pH of at least 9.5.

The colour of the soap obtained from this process is convenientlymeasured on a 5.84% w./v. aqueous solution of the soap (dry basis) withthe aid of a Lovibond Tintometer using a Lovibond 13.3 cms. cell. Theacceptable standard of colour depends on the purpose to which the soapproduced is to be applied. The colour is determinable in terms ofLovibond red and yellow unitsthese units being combined to form onevalue (referred to in this specification as the soap colour) by use ofthe formula:

soap colour= (yellow reading) +30 X (red reading) ice The term soapcharge, as defined in this specification refers to the material obtainedby saponification of a suitable charge of fat and alkali. The term fatmay refer to an animal tallow, a vegetable oil such as palm oil, palmkernel oil or coconut oil, a fish oil or to the fatty acids obtainedfrom such materials by a conventional splitting technique. Mixtures ofthese fats may be used in the process of this invention-a convenientmixture, for example, being based on tallow and up to 20% W./w. of anoil such as coconut oil. These fats are henceforth referred to in thespecification as the fat charge. When the fat charge is of a low grade,it is desirable that it be given a pre-treatment with an activated earthor other adsorbent bleaching agent (referred to henceforth in thisspecification as a standard bleaching treatment) before saponification,as the colour thus removed will not then compete with the unsorbedmaterial for the borohydride. The colour of a bleached low grade tallowmay vary from 40 yellow, 0.8 red to 15.0 yellow, 2.5 red (when measuredin a 0.635 cm. cell of a Lovibond Tintometer).

Synthetic fatty acids, such as those obtained by the oxidation ofparaflinic hydrocarbons, may also be used in the process of thisinvention alone or in admixture with a fat.

A soap charge prepared from a toilet grade standard bleached tallow orthe soap obtained from such a tallow may also be treated by the processof this invention particularly when it is desired to obtain a productessentially free of odoriferous compounds.

The term alkali metal in this specification is to be taken as referringto lithium, potassium, or sodium. Of the alkali metal borohydrides, thesodium derivative is commercially most readily available. The alkalimetal borohydride may be added in the process of this invention eitherin solid form, or as an aqueous solution, or as a blend with soap, or itmay be formed in situ from other borohydrides. Preferably it is added asa solution in aqueous alkali-suitable alkalies being sodium hydroxide orpotassium hydroxide.

By in situ formation of an alkali metal borohydride is meant theaddition of a borohydride salt, other than an alkali metal salt, to asoap containing system. Due to the large excess of alkali metal ionswhich are present in such a system, the borohydride salt will beconverted to the alkali metal borohydride.

The alkali metal borohydride is conveniently added either towards theend of the saponification stage of the soap manufacture or after thesaponification has been completed, as, at these points, the pH of thesaponification system does not vary so widely as during the initialperiod of saponification.

If the borohydride is added during the saponification stage, boiling ofthe saponification system should be continued for a further period ofabout 30 minutes to ensure complete dispersion of borohydride andmaximum reduction of colour and odour of the soap charge. The totalcolour and odour reduction is dependent on the effectiveness with whichthe borohydride is spread through the saponification system as well asthe level used.

Colour and odour removal can also be effected after the completion ofsaponification as long as the soap is still in a fluid state ot permitadequate mixing with the borohydride and as long as the pH of the soapdoes not fall below about 9.5, a preferred range of pH being 9544.0.

The alkali metal borohydride is preferably added immediately after thesoap derived from the saponification process has been washed orimmediately prior to the stage when the soap is dried. Alternatively itis possible to add the borohydride to the soap immediately after the endof 3 the drying stage or at the milling stage (with accompanyingpigment.)

It is necessary to ensure that the temperature of the soap containingsystem is adequately controlled and that there is sufficient alkalipresent in the soap-containing system to allow time for the borohydrideto disperse completely and to carry out its reducing action beforedecomposition. If the borohydride is to be mixed with a soap containingsystem that is being stirred with normal paddle-type stirrers andmaintained at 90-100 C. it is preferable that the pH be at least12.0-14.0. With continuous or semi-continuous processing where moreefiicient inline mixing is employed pH control need not be quite sostringent.

The amount of alkali metal borohydride to be used for the improvement ofthe colour and odour of soap, preferably lies within the range of0.005-0.30% by weight of the total fatty acid content of the soap used.A particularly preferred amount of borohydride for the treatment of asoap obtained from a toilet grade standard bleached tallow lies withinthe range 0.02-0.10% by weight of the fat charge. Addition ofborohydride in excess of 0.30% by weight of the fat charge is, ofcourse, also effective but is less likely to be economically attractive.

Borohydrides decompose in aqueous media with the formation of borate ionand hydrogen. Adequate precautions should be taken in view of possiblefire hazards associated with the evolution of hydrogen and theassociated problem of foam formation. The foam formation may becontrolled by (a) gradual addition of the borohydride to the soapcontaining system in a vessel having a volume sufiicient to allow forany expansion of the soap containing system or (b) adding theborohydride to the soap immediately prior to the stage when it is to bepumped into a drier unit and to maintain the soap in this drier unitunder pressure until it is sprayed onto a further processing unit Theinvention is now further illustrated with reference to the followingexamples.

EXAMPLE 1 A low grade tallow was treated with four different percentageproportions (ranging from 1-6% w./W.) of fullers earth for 5 minutes at105 1l0 C. followed by 5 minutes at 110-115 C. After filtration from thefullers earth, the tallows obtained from each of the four bleachinglevel experiments were divided into three aliquots in beakers, eachaliquot containing 20 parts by weight of bleached tallow. After meltingthese samples of tallow on a boiling water bath, 10 parts by volume of a30% w./v. aqueous sodium hydroxide solution were added to the firstsample from each bleaching level experiment. This mixture was maintainedon the boiling water bath and stirred until completely saponified. 9parts by volume of the 30% w./v. aqueous sodium hydroxide solution wereadded to the remaining two samples from each bleaching level experiment.These mixtures were subsequently similarly saponified.

minutes after the addition of the sodium hydroxide solution, one part byvolume of 30% w./v. aqueous sodium hydroxide solution containing 0.01part by weight of sodium borohydride was added with stirring to thesecond sample of each of the saponifying bleached tallows. One part byvolume of 30% w./v. aqueous sodium hydroxide solution containing 0.02part by weight of sodium borohydride was similarly added to the thirdsample of each of the saponifying bleached tallows.

After one hour, 10 parts by volume of water were added to each of the 12saponified samples and the mixtures thus obtained were homogenised byrapid stirring. The homogenised mixtures were then transferred to largerbeakers, 290 parts by volume of distilled water added to each and thesoap dissolved by heating to about 75 C. The colour of each of thederived soap solutions was determined by Lovibond colorimetry in a 13.3cms. cell.

(such as a vacuum chamber or a chilling drum) or 40 The results obtainedwere tabulated as below:

Percent bleaching earth 1 2 4 6 Percent sodium borohydride.. 0 0.05 0.10 0.05 0 0.05 0 0.05 0.1 Lovibond Yellow 29 27 15 7.4 6.3 4.0 3.2 2.81.5 1.5 Lovibond Red 1.0 1.0 0 8 1.6 1.0 0.8 0.6 0.6 0.3 0.2

(0) adding the borohydride to the soap as it leaves the EXAMPLE 2washing unit and degasing by spraying the treated soap into the fittingpan.

Borate ion is readily removable from the treated soap by aqueous washingalthough its presence has no deleterous effect on the soap or anymaterial (such as perfume) that is to be added to the soap at a laterstage in its preparation. A further advantageous feature of the processof this invention lies in the fact that it is so readily incorporatedinto a normal soap manufacturing process. Flame-proofing of thesoap-making machinery may be necessary in view of the possible hazardassociated with the evolution of small volumes of hydrogen.

The amount of adsorbent agent used in the standard bleaching treatmentof a low grade fat charge is preferably about 6% by weight of the fatcharge. Fullers earth is a preferred bleaching agent, but otheradsorbent earths or bleaching carbons may be used.

The colour and odour of the treated soap depends on the amount and typeof adsorbent bleaching agent (if any) that is usd in the pre-treatmentof the fat charge, the amount of alkali metal borohydride used, the timeand temperature of the treatment with the borohydride, the pH of thesoap containing mixture during the borohydride treatment and theefficiency of mixing the soap containing mixture.

A further beneficial effect that is obtained when the borohydride isadded during the saponification stage is that the derived glycerine lyeis almost water white.

A fat charge containing 92.5% w./w. tallow (that had been bleached bytreatment with 6% W./W. adsorbent earth) having a Lovibond Yellowreading of 11.7 and a Lovibond Red reading of 1.4 in a 5.1 cm. cell and7.5% w./w. coconut oil was saponified at C. in a conventional soap pan.The soap thus prepared was separated from the lye and washed, in aconventional washing unit, with brine containing 1% w./v. sodiumhydroxide. As the washed soap passed out of the washing unit it wastreated with an amount of aqueous 5.0% w./v. sodium hydroxide solutioncontaining 10 w./ w. sodium borohydride-sufiicient to provide 0.1%sodium borohydride based on the weight of the fat charge originallysaponified. The borohydride treated soap was subsequently fitted,neutralised, heated and dried according to standard practice.

The soap colour of the soap prepared in the above experiment was 37,while the soap colour of a soap prepared from a similar fat charge whichwas not treated with borohydride, was 60.

In a further experiment the soap was washed with brine containing 2%w./v. sodium hydroxide. The soap colour of the untreated soap was 54.The colour of the soap that had been treated with 0.1% w./w. sodiumborohydride was 43.

Hydrogen evolution inflated the 20 tons of soap that were prepared ineach of the above experiments where borohydride was used, to the volumethat would have been occupied by 35 tons of soap.

EXAMPLE 3 A fat charge containing 92.5% w./w. tallow (that had beenbleached by treatment with 6% w./w. adsorbent earth) having a LovibondYellow reading of 6.0 and a Lovibond Red reading 0.9 (measured in a 5.1cm. cell), pan. 7.5% w./w. coconut oil was saponified at 95 C. in aconventional soap pan. The soap thus prepared was separated from the lyeand subsequently washed with brine containing 1% w./v. sodium hydroxide.Aqueous 5% w./v. sodium hydroxide solution containing w./w. sodiumborohydride (in an amount sufiicient to provide 0.02% sodium borohydrideby weight of the original fat charge) was added to half the soap as itleft the washing unit. The soap colour of the soap treated in this waywas 26=(1.4 Y+0.4 R). The soap colour of the remaining soap that had notbeen treated with sodium borohydride was 39=(2.1 Y+0.6 R).

EXAMPLE 4 A 1.5 ton soap charge was prepared by saponification of a fatcharge comprising 85% w./w. tallow and w./w. coconut oil. The lye wasseparated from this soap charge and the soap washed with brinecontaining 1% w./v. sodium hydroxide, fitted and passed on to the heatexchanger unit prior to drying, milling and plodding.

Sodium borohydride was dissolved in cold aqueous 4% -w./v. sodiumhydroxide solution in an amount sufficient to provide a 15 w./w.solution. Sufiicient of this solution was used to provide an amount ofborohydride equal to 0.1% by Weight of the fat charge. This solution wasinjected into the soap line immediately before the pump feeding the heatexchanger unit over a period of 30 minutes. Samples of the treated soapwere taken, after they had been dried, milled and plodded and examinedfor free alkalinity and soap colour. Comparative samples of untreatedsoap were similarly examined.

The problem of foaming was largely overcome by this process.

EXAMPLE 5 A 250 lb. fat charge comprising 80% w./w. toilet gradestandard bleached tallow and w./w. standard bleached coconut oil wassaponified. The soap thus obtained was separated from the lye, washedand fitted. The soap thus obtained had a free alkali content of 0.01%.

A 40 lb. sample of this soap was heated to 90 C. 750 mls. of a 10% w./w. sodium borohydride solution in aqueous 5% w./v. sodium hydroxidesolution was gradually added to the heated soap with stirring(representing an addition of 0.1% sodium borohydride based on the weightof fatty material present in the soap). A further 420 mls. aqueous 5%w./v. sodium hydroxide solution (increasing the amounts of free alkalito 0.5% w./v.) was also added to the soap containing system to reducethe amount of foaming.

A further 40 lb. sample was similarly treated with half the volume ofborohydride solution.

The treated soap was fitted, milled and plodded and its odour evaluatedby a panel of assistants who were asked to smell the soaps with closedeyes (thus to prevent any influence of colour difference) and to expressan opinion as to which soap had the stronger odour. Since the sampleswere unperfumed the assessment of the panel members was a direct measureof the strength of the undesirable base odour. Each entry was scored +1for the tablets with the stronger odour, 0 for no difference and -1 forthat which had the weaker odour. The scores for each panel member foreach soap were added together to arrive at the total score for eachsoap. A low score indicated little base odour and a high score indicatedstrong base .odour.

The experimental designs contained soap bars not relevant to the presentinvention and the results on these soap bars were extracted. The odourscores for any one series did not therefore lie about the zero mean asthey would have done in a complete pad comparison analysis.

Addition of borohydride: Odour score Standard error :15.7

A difference of twice the standard error is significant at the 5%probability level.

EXAMPLE 6 A further 40 lb. sample of the soap prepared in Example 5' washeated to C. 880- mls. of a 10% w./w. potassium borohydride solution inaqueous 5% w./v. sodium hydroxide solution was gradually added to thesoap with stirring (representing an addition of 0.08% w./w. potassiumborohydride based on the weight of the fat charge). A further 320 mls.aqueous 5% w./v. sodium hydroxide solution (increasing the amount offree alkali to 0.5% w./v.) was added to the soap to reduce the amount offoaming.

This experiment was repeated with three further 40 lb. samples of thesoap prepared in Example 5, with the exception that the amount of thepotassium borohydride solution added was reduced. The amounts ofpotassium borohydride used in each case, amounted to 0.02%, 0.04% and0.06% by weight of the fat charge, respectively The odour value of eachsample was assessed as follows:

A panel of 10 people was asked to compare the odour of samples of thesoaps treated by the process described in this example, with-a sample ofuntreated soap and to place each sample according to the degree ofdeodorisation they thought had been achieved. The following table showsthe number of people who were able to correctly allot the right positionfor each sample.

Percent borohydride: No. of correct allotments What is claimed is:

1. In a process for the production of a soap comprising the stages of(a) reacting a fat charge with an alkali,

(b) separating, washing and fitting a soap containing system obtainedfrom stage (a) (c) drying and milling the soap containing system and (d)extruding the dried soap, the improvement which comprises adding analkali metal borohydride at a pH of at least 9.5 at any stage of saidprocess up to the step of extruding the dried soap.

2. A process as claimed in claim 1 in which the treatment with thealkali metal borohydride is carried out at a pH between 9.5 and 14.0.

3. A process as claimed in claim 1 in which the soap is produced from afat charge, the main constituent of which is tallow.

4. A proces as claimed in claim 1 in which the soap is produced from afat charge, a constituent of which is palm oil, palm kernel oil orcoconut oil.

5. A process as claimed in claim 1 in which the soap is produced from afat charge, the constituent of which is the fatty acids obtained fromfat by a conventional splitting technique.

6. A process as claimed in claim 1 in which the fat charge ispre-treated with an adsorbent bleaching agent.

7. A process as claimed in claim 1 in which the soap is treated with analkali metal borohydride after the reaction of the fat charge withalkali is completed.

8. A process as claimed in claim 1 in which the soap is treated with analkali metal borohydride immediately after it has been washed.

9. A process as claimed in claim 1 in which the soap is treated with analkali metal borohydride immediately prior to the drying stage.

10. A process as claimed in claim 1 in which the soap is treated with anamount of alkali metal borohydride equal to 0.005-0.30% by weight of thefat charge.

11. A process as claimed in claim 1 in which the soap is treated with anaqueous sodium hydroxide solution of an alkali metal borohydride.

12. A process as claimed in claim 1 in which the soap is treated withsodium borohydride.

References Cited UNITED STATES PATENTS 2,946,813 7/1960 Palmquist 260417LEWIS GOTTS, Primary Examiner E. G. LOVE, Assistant Examiner US. Cl.X.R. 260417

